Apparatus for obtaining liquid oxygen



March 13, 1956 R. BECKER ET AL APPARATUS FOR OBTAINING LIQUID OXYGENFiled Nov. 9, 1954 United States Patent Ofiice APPARATUS FOR OBTAININGLIQUID OXYGEN Rudolf Becker, Munich-Solln, and Wilhelm Hartmann,

Pullach, near Munich, Germany, assignors to' Gesellschaft fiir LindesEismaschinen Aktiengesellschaft, Hollriegelskreuth, near Munich, GermanyApplication November 9, 1954, Serial No. 467,816 Claims priority,application Germany December 24, 1953 3 Claims. (Cl. 62-123) The presentinvention relates to an apparatus for obtaining liquid oxygen.

In installations for obtaining liquid oxygen from air,

the cold loss occurring with the removal of oxygen in liquid formaccording to the former state of the art is compensated in that the airto be decomposed is supplied at high pressure and the cold outputobtained in the ex- Pflllsion of the air is used to proceed from thefact that the cold losses are particularly slight if the total quantityof gas to be treated is small. However, it is necessary according tothis method to employ relatively expensive counter-current heatexchangers, since, at high pressures, regenerators providing a betterexchange cannot be used practically, owing to excessively high gaslosses. It is an object of the present invention to provide an apparatusto obtain liquid oxygen by the rectification of compressed air liquefiedat low temperatures, comprising a turbo-compressor to compress air to apressure of between 3 and atmospheres excess pressure, two periodicallychanged-over regenerators connected at their upper end portions to theturbo-compressor, a separating column to decompose the cold air supplythereto mainly into oxygen and nitrogen, a first and secondheatexchanger connected successively in series between the regeneratorsat the lower end portions thereof and the separating column at the upperend portion thereof, the combination of a third heat-exchanger and anexpansion turbine connected successively in series between, theregenerators also at the lower end portions thereof and the separatingcolumn at a location intermediate the ends thereof, a separator forliquid oxygen'connected, at its upper end portion to the lower endportions of the regenerators and at its. lower end portion to the upperend portion of the separating column through the second heat-exchanger,and a fourth and fifth heat-exchanger located within the regeneratorsand connected at the top ends thereof successively through the thirdheat-exchanger, the bottom of the separating column and the secondheatexchanger to the top of the separating column, and, at the lower endportions thereof, through the first heatexchanger to the upperend-portion of the liquid oxygen separator.

It is also an object of the present invention to provide a process forobtaining liquid oxygen by the rectification of compressed air liquefiedat low temperatures, comprising the steps of succesively compressing theair to a non-uniform pressure of between 3 and 15 atmospheres excesspressure, cooling the compressed air in regenerative heat-exchange withdecomposition products separated therefrom, dividing the cold,compressed air into a major and a minor fraction, partially warming themajor fraction in heat-exchange with the previously warmed minorfraction, expanding the said major fraction to produce useful work,separating the expanded air mainly into oxygen and nitrogen, partiallyliquefying the minor fraction partly by cooling in heat-exchange withthe cold, essentially nitrogen-containing gaseous mixture and partly bysuccessive warming in parallel- 2,737,784 a Patented Mar.'13, 1955current heat-exchange with a warm, compressed air before the divisionthereof into a major and a minor fraction, and in counter-currentheat-exchange with the major fraction before the expansion thereof,cooling in heatexchange with liquid oxygen and with a cold, essentiallynitrogen-containing gaseous mixture, separating the resulting liquid airmainly into oxygen and nitrogen, and supplying cold, essentiallynitrogen-containing gaseous mixture from the air separation to cool andpartially to liquefy said minor air fraction and to cool the warm,compressed air in regenerative heat-exchange.

This method of operation affords substantial advantagcs, for, at lowpressure, shaking regenerators can be used, which enable particularlyeflicient heat-exchange to be obtained, since they operate withremarkably small temperature differences between the entering andissuing media undergoing the heat-exchange operation. By correctlydimensioning the regenerators and by correctly adjusting the gasquantities which are exchanging heat, it is possible to ensure that, atthe warm end of the regenerators, the mean temperature of the enteringair is only approximately one degree or less higher than the meantemperature of the issuing nitrogen. Thus, the cold losses throughincomplete heat-exchange are correspondingly small and it is no longer adecisive matter to keep to a minimum the quantity of air passed throughthe apparatus per unit of liquefied oxygen produced. This also permits asimpler construction and maintenance. The use of regenerators alsosolves the problems of water and carbon dioxide separation in a verysimple way.

The energy required for an installation operating according to thisprocess is approximately 10% greater than for an installation in whichhigh-pressure is allowed to expand. However, the simpler construction ofthe apparatus and the simpler attention required, together with thepossibility of going over to larger units (without the necessity ofsubdividing the compressor equipment into a plurality of units) andother advantages indicated hereinafter are more than sufiicient tobalance the somewhat higher energy requirement. There are also otherfactors which make the use of the above-described process advantageous.In particular, the fact that, with the earlier installations, for arelatively high output it was necessary to increase appropriately thenumber of piston compressors providing the higher pressure. (Highpressure compressors are normally built only up to outputs ofapproximately 1,000 m. /h.) But this not only requires space andbuildings but also leads to an'increased outlay in attention andmaintenance. In some circumstances, the interruptions in operation owingto trouble in the running of the plant can be a heavier item thanrepairs and additional running costs. In addition, turbo-compressors andturbines exhibit an improved degree of efficiency with increased output,in contrast to piston compressors, whose degree of efiiciency does notrise with increased size. It should also be borne in mind thatturbo-machines (rotary compressors and, more particularly, expansionturbines) have just recently been so improved that their degree ofefficiency, e. g. for expansion turbines, has risen from 70% to overThis means that the energy differences will be even less than before, orwill disappear completely.

In view of the above, it is obvious that the present process issubstantially more eflicient than the known processes.

A particular advantage is that the liquid oxygen obtained is absolutelyoil-free, since the air to be decomposed does not come into contact inthe turbo-compres sors and turbines with lubricated surfaces.

For a better understanding of the invention and to shown how the same isto be carried into effect, reference will now be made to theaccompanying drawing, in which:

An apparatus and process for obtaining liquid oxygen from air areillustrated schematically by a flow diagram.

The whole of the air to be treated is compressed to a pressure ofapproximately 6 atmospheres absolute in a turbo-compressor 1,intensively cooled by one of two regenerators 3, 4 (3 in the caseshown), partially warmed in a first heat-exchanger 5 in heat-exchangewith warmer air, allowed to expand and produce work in a turbine 6 andsupplied to a separating column 7. A portion of the air intensivelycooled in the regenerator 3 is branched off at 8, passed through aseparator 9, and a second heat-exchanger 19, from which condensate canflow back to the separator 9, and partially reheated in a third andfourth heat-exchanger 10 and 11 within the regenerators 3 and 4, whichare expediently filled with loose material. It is then led through thefirst heat-exchanger 5, liquefied by heat-exchange with a bath of liquidoxygen in a liquefier 12 at the foot of the separating column 7, ledthrough a fifth exchanger 18 and, after combination (at 13) with etherliquid, air, delivered as wash liquid at the head of the column 7 (at14). The valve 2 serves as a by-pass valve for a part of the air, whichcan be conveyed parallel to the exchangers 10, 11 and 5 for regulatingthe air pre-warming before the turbine.

The liquid air separated in the exchanger 19 and conveyed back orcollected in the separator 9 is removed, cleaned by a filter 15 for thepurpose of separating out impurities such as carbon dioxide and ice and,after being allowed to expand in a valve 17, is combined at 13 with theother liquid air from the liquefier 12, which is allowed to expand bymeans of the valve 16.

Nitrogen, which still contains approximately 10% of oxygen, is allowedto escape from the top of the column 7, brought into heat-exchange inthe exchanger 18 with the liquid air which has been liquefied in theliquefier 12 and taken from the separator 9 and, after passing throughthe exchanger 19-where it liquefies further quantities of air-isconveyed out through the second of the two regenerators 3, 4 in the caseshown and warmed in so doing. Oxygen which is produced in the separatingcolumn 7 is removed in the liquid state at 20.

-As usual, the regenerators 3, 4 are switched over at regular intervals,so that the air flows alternately through the regenerators 3 and 4 andthe nitrogen alternately through the regenerators 4 and 3. The removalof part of the air after the regenerators, in order to heat it again inthe exchangers 10 and 11, is chiefly carried out for the purpose ofheating the main quantity of air before the expansion turbine 6 in orderto increase its efiiciency and to prevent liquefaction therein. By thismeans, the branched-off part quantity of air, being removed after theregenerator, has the same purity from carbon dioxide and water as thenon re-warmed quantity of air. The

4 tubular heat-exchangers 10 and 11 within the'regenerators can bedispensed with if the air used to heat the turbine air is branched offin a relatively warm region of the regenerators, and purified in amanner known per se by passage through one of two alternately operatedadsorbers.

A valve 21 serves to regulate the quantity of air passing through thecolumn.

We claim:

1. An apparatus to obtain liquid oxygen by the rectification ofcompressed air liquefied at low temperatures, comprising aturbo-compressor to compress air to a pressure of between 3 and 15atmospheres excess pressure, two periodically changed-over regeneratorsconnected at their upper end portions to the turbo-compressor, aseparating column to decompose the cold air supply thereto mainly intooxygen and nitrogen, at first and second heatexchanger connectedsuccessively in series between the regenerators at the lower endportions thereof and the separating column at the upper end portionthereof, the combination of a third heat-exchanger and an expansionturbine connected successively in series between the regenerators alsoat the lower end portions thereof and the separating column at alocation intermediate the ends thereof, a filter for liquid airconnected at its upper end portion to the lower end portions of theregenerators and at its lower end portion to the upper end portion ofthe separating column through the second heat-exchanger, and a fourthand fifth heat-exchanger located within the regenerators and connectedat the top ends thereof successively through the third heat-exchanger,the bottom of the separating column and the second heat-exchanger to thetop of the separating column, and, at the lower end portions thereof,through the first heat-exchanger to the upper end-portion of the liquidoxygen separator.

2. An apparatus as claimed in claim 1, wherein a valve 21 is furtherprovided connected between the conduit from the expansion turbine to theseparating column and the conduit from the upper end portion of theseparating column to the second heat-exchanger.

3. An apparatus as claimed in Claim 1, wherein there is further provideda filter for liquid oxygen connected between the lower end portion ofthe liquid oxygen separator and the upper end portion of the separatingcolumn.

References Cited in the file of this patent UNITED STATES PATENTS2,619,810 Rice Dec. 2, 1952 2,650,481 Cooper Sept. 1, 1953 2,664,719Rice Jan. 5, 1954 2,671,324 Trumpler Mar. 9, 1954

1. AN APPARATUS TO OBTAIN LIQUID OXYGEN BY THE RECTIFICATION OFCOMPRESSED AIR LIQUEFIED AT LOWER TEMPERATURES, COMPRISING ATURBO-COMPRESSOR TO COMPRESS AIR TO A PRESSURE OF BETWEEN 3 TO 15ATMOSPHERES EXCESS PRESSURE, TWO PERIODICALLY CHANGED-OVER REGENERATORSCONNECTED AT THEIR UPPER END PORTIONS TO THE TURBO-COMPRESSOR, ASEPARATING COLUMN TO DECOMPOSE THE COLD AIR SUPPLY THERETO MAINLY INTOOXYGEN AND NITROGEN, A FIRST AND SECOND HEATEXCHANGER CONNECTEDSUCCESSIVELY IN SERIES BETWEEN THE REGENERATORS AT THE LOWER ENDPORTIONS THEREOF AND THE SEPARATING COLUMN AT THE UPPER END PORTIONTHEREOF, THE COMBINATION OF A THIRD HEAT-EXCHANGER AND AN EXPANSIONTURBINE CONNECTED SUCCESSIVELY IN SERIES BETWEEN THE REGENERATORS ALSOAT THE LOWER END PORTIONS THEREOF AND THE SEPARATING COLUMN AT ALOCATION INTERMEDIATE THE ENDS THEREOF, A FILTER FOR LIQUID AIRCONNECTED AT ITS UPPER END PORTION TO THE LOWER END PORTIONS OF THEREGENERATORS AND AT ITS LOWER END PORTION TO THE UPPER END PORITON OFTHE SEPARATING COLUMN THROUGH THE SECOND HEAT-EXCHANGER, AND A FOURTHAND FIFTH HEAT-EXCHANGER LOCATED WITHIN THE REGENERATORS AND CONNECTEDAT THE TOP ENDS THEREOF SUCCESSIVELY THROUGH THE THIRD HEAT-EXCHANGER,THE BOTTOM OF THE SEPARATING COLUMN AND THE SECOND HEAT-EXCHANGER TO THETOP OF THE SEPARATING COLUMN AND, AT THE LOWER END PORTIONS THEREOF,THROUGH THE FIRST HEAT-EXCHANGE TO THE UPPER END-PORTION OF THE LIQUIDOXYGEN SEPARATOR.